US2290075A - Thermal process and device for surveying the beds traversed by drill holes - Google Patents

Description

M. SCHLUMBERGER 2s THERMAL PROCESS AND DEVICE FOR SURVIYIJNG- THE BEDS TRVERS'ED BY A DRI-LL HOLE Filed April 3. 1939 v2 shams-sheetV 1 INVENTOR.

ATTORNEYS ,Pafenf july 14, 1942 THERMAL PROCESS AND DEVICE FOR SUR- VEYING THE BEDS TRAVERSED BY DRILL HOLES Marcel Schlumberger, Paris, France, assignor, by

mesne assignments, to Schlumberger Well Surveying Corporation, Houston, Tex., a corporation of Delaware Application April 3, 1939, Serial No. 265,742

In France April 8, 1938 8 Claims.

This invention relates to methods and apparatus for determining the nature of earth formations traversed by 'a bore hole. More specifically, it relates to an improved method and apparatus for determining the nature of earth formations by obtaining indications of their thermal properties.

It is well known that the earth formations traversed by a drill hole may be readily distinguished by their relative thermal properties. For example, porous formations permeated with fluid are generally characterized by a high apparent thermal conductivity, caused apparently by convection currents produced in the uid permeating the formations when the latter are brought into contact with a medium of different temperature. the other hand are generally characterized by low thermal conductivity probably because their fiuid content is low and the iniiuence of convection currents is correspondingly reduced.

Impervious' formations on' to provide an improved method and apparatus for determining the thermal properties of earth formations traversed by a bore hole in which heat is generated uniformly in an extended portion of the bore hole, enabling the nature of the formations to be obtained in a simple and effective manner, and with greater accuracy than has been possible heretofore.

A further object of the invention is to provide a method and apparatus of the above character in which the heating element is maintained in a fixed position in the bore hole and in which bore hole temperature measurements are made by moving a temperature responsive device through the bore hole in the portion influenced by the heating element.

The method of the invention comprises esseni tially the steps of heating in situ the liquid con- Processes are already known for measuring I the thermal properties of the strata traversed by a bore hole. In one such method, for example, it is proposed to fill the hole with liquid having a temperature considerably different from .the natural tempera-ture of the formations traversed by the bore hole. After allowing the heat contained in the uid to flow into the strata surrounding the bore hole for a given period of time, the variation of the temperature of the bore hole i'luid with depth is determined, from which the relative thermal properties of the surrounding formations may be ascertained.

. While this method does provide useful information about the nature oftheearth formations, it has been found to be somewhat unsatisfactory because it necessitates emptying the bore hole and refilling it with uid of higher temperature than the natural temperature of the beds and is, therefore, costly and time consuming.

It has also been proposed to generate heat in a localized zone in a bore hole, thereafter measuring the temperature of the bore hole liquid in order to obtain information about the thermal properties of the strata surrounding the, bore hole. This method also gives valuable information, but it has been found that the results are somewhat modied due to the. fact that the heating element and the temperature measuring device are moved through the bore hole together, so that the thermal distribution in the bore hole fluid is disturbed and not uniform.

f The principal object of the present invention is tained in an extended portion of the drill hole, 'l

and obtaining indications'of temperature variations in the bore hole fluid resulting from the absorption of heat therefrom by the formations surrounding the bore hole. In the neighborhood of porous beds, considerable quantities of heat are absorbed from the bore hole fluid in a given period of time, so that the temperature `of the bore hole uid near such beds remains relatively unchanged. Adjacent impermeable formations',v

however, relatively little heat is absorbed from the bore hole fluid, so that its temperature tends to rise. Accordingly, by measuring the temperature variations in the fluid contained in the bore hole, the thermal properties of the surrounding formations may be readily determined.

Inasrnuch as the temperature of the formations surrounding the bore hole normally tends to increase with depth, it is ordinarily desirable to malge a temperature run before the fluid in the bore hole has been heated, in order to provide a standard of comparison withwhich subsequent temperature measurements may be compared. z

The heatingy of the bore hole fluid may be accomplished in any known manner, provided only that the quantity of heat generated is equally distributed along the portion of the bore hole being investigated. Thus, chemicals may be lowered into the bore hole for the purpose of producing exothermic chemical reactions therein in order to generate heat. It is preferred, however, to generate heat in the bore hole by passing current through electrical resistances, which may be immersed in the bore hole fluid.`

The invention may be better understood from the following detailed description, taken in conconstructed in accordance with the invention,

for determining the thermal properties surrounding an uncased bore hole;

Fig. 2 is a curve of temperature against depth in the bore hole, illustrating the manner in which porous strata may be readily identified;

Fig. 3 is a schematic diagram of a modification,l

of the apparatus illustrated in Fig. l; and

Fig. 4 is a. schematic diagram of apparatus constructed in accordance with the invention for determining the thermal properties of formations surounding a cased and cemented drill hole.

Considering the embodiment illustrated in Fig. 1, an impervious formation 10 of relatively low thermal conductivity is shown, above a. porous formation II of relatively high thermal conductivity, beneath which lies a second impervious formation I2 also of relatively low conductivity, all three formations being penetrated by a bore hole I3. The drill hole I3 contains the liquid or mud I4 which should preferably be viscous enough to prevent the transmission of heat by convection parallel to the axis of the drill hole, but yet not so viscous as to prevent the equalization of the temperature in any given portion of the bore hole.

The heating element may comprise, for example, an elongated wire I5 which is bent back on itself, and whose upper ends I6 and I'I are connected to a pair of conductors I8 and I9 of relativelylarge cross-section. The conductors I8 and I9 are contained in an insulated cable 20, which passes over a sheave 20' and which is wound in the usual manner upon a winch 2l, by means of which the heating element I5 maybe raised and lowered in the bore hole.

The ends of the conductors I8 and I9 may be connected to the slip rings IB' and I9' which in turn are connected through the brushes 2| vand 22' and the wires 28 and 29, respectively, to a source of current' 30 which provides velectrical energy for generating heat in the heating element I5. In some cases, however, considerable heat losses may arise due to the high intensity bore hole may be measured by any suitable temperature measuring device 22, such as for example, the temperature measuring devices disclosed in United States Patents Nos. 2,249,751 and 2,238,015 to H. G. Doll, issued July 22, 1941,'and April 8, 1941, respectively. 'I'he ternperature measuring' device 22 is adapted to be moved through the bore hole I3 by the cable 23 which passes over a sheave 24 and which is wound on an auxiliary winch 25 at the earth's I surface in the usual manner,

current flowing through the conductors I8 and I9 in that part of the cable 29 wound on the winch 2I.

To avoid possible damage to the cable, therefore, and to eliminate the power losses in this part of the cable, it may be preferable to connect the wires 28 and 29 directly to cable 20 at a place between the winch and the mouth of the bore hole, as shown in Fig. 3. This may be accomplished by stripping a small portion of the insulation from the cable 20 and connecting the wires 28 and 29 to the conductors I8 and I9 at 26 and 21, respectively.

Where this alternative is used, it is possible to dispense with the wires of large cross-section I8 and I9 in which case the heating element I5 will be directlyconnected to the source 30 at the surface of the earth. Where this is done, however, the heating element I5shou1d be of suilicient length to reach the lowest depth at which measurements of temperature are contemplated.

The heating element I5 is preferably made equal in length to the length of the portion of the bore hole which it is desired to investigate and since it comprises a uniform wire of constant resistance, it generates heat uniformly at a constant rate along its entire length.

The temperature of the liquid contained in thel The measured temperatures may be recorded in the bore hole on a strip of lm, for example, in which case the temperature measuring device 22 should be a recording instrument. If desired, however, the temperature measuring device 22 may be connected to a pair of conductors within the cable 23 (not shown) through the slip rings 24 and 25', respectively, and the wires 26' and 21', respectively, to a measuring or recording instrument 39 located at the earths surface, as indicated in Figs. l, 3 an'd 4.

In operationy a preliminary temperature survey may be made by lowering the temperature measuring device 22 through the bore hole, from which the curve A (Fig. 2) is obtained. It will be noticed that this curve is substantially a sloping line, indicating that the temperature of the bore hole uid normally increases with depth. The heating element I5 is then lowered by means of the winch 2| to the desired position in the bore hole I3 at which position it is maintained during the heating step. If the connections between the heating element `I5 and the source of current 3U are made as indicated in Fig. 1, then the heating element I5 will begin to generate heat as soon as the current so'urce 3D is operated.

On the other hand, if the heating element I5 is to be directly connected to the source of current 30 at the surface of the earth, as indicated in Fig. 3, part of the insulation is stripped oi the cable 20 and the wires I8 and I9 are connected at 26 and 21 through wires 28 and 29 to a source of current 30. As pointed out above, by making the connection between the current source 30 and thecables I8 and I9 in this manner, a considerable saving in power results because heat losses produced by the passage of current through the length of the cable on the winch 2I are eliminated. The heating element I5 now begins to generate heat uniformly at a constant rate over its entire length.

It will be understood that heat need not be generated at a constant rate during the run, but the rate of generation might vary as a function of time, provided that heat is generated uniformly over the entire portion of the bore hole being investigated.

In the neighborhood of impermeable beds of relatively low vapparent thermal conductivity, the greater part of the heat generated accumulates in the liquid contained in the bore hole, s o that its temperature tends to rise above the normal value. In adjacent beds of higher apparent thermal conductivity such as, for example, porous beds, the heat generated is almost entirely transmitted through the bed and relatively little remains in the liquid contained in the drill hole. Accordingly, the bore hole liquid temperature .remains substantially unchanged, or increases very slowly.

The heating step is continued until beds of relatively high thermal conductivity may be readily differentiated from beds of relatively low thermal conductivity by observing variations in the temperature of the liquid contained inthe bore hole. The temperature measuring device 22 is then moved through the bore hole overv the length under investigation and a curve similar to curve Bv (Fig. 2) is obtained. It will `be noted from this curve that adjacent the impermeable beds IIJ and I2 of relatively low thermal conductivity, the temperature of the bore hole iluid is considerably greater than the normal bore hole temperature, as indicated by curve A, whereas in the neighborhood of the porous formation Il, it is only slightly higher than the normal bore hole temperature for this particular region, as indicated by curve A.

Inasmuch as the casing with which the bore holes are usually provided does not interfere I claim: 1. The method of determining the nature of earth formations traversed by a bore hole which comprises the steps of generating heat uniformly and simultaneously along an extended portion of the bore hole, and obtaining -indications of the rate of transmission of the generated heat through the formations surrounding the bore hole in said portion, whereby their relative thermal properties may be ascertained.

'2. Themethod of determining the nature of earth formations traversed by a bore hole which comprises the steps of generating heat uniformly indications of temperature variations in said por-A substantially with the heat exchange between the fluid in the bore hole and the surrounding strata, the method'of the invention may be readily applied to cased bore holes as well as uncased holes. It has been found that the presence of the casing merely modifies the shape of the curve obtained by smoothing out the irregularities. It is believed that this results because in a cased hole, a larger proportion of heat is transmitted in a direction parallel to the axis of the bore hole than where no casing is present. The method may likewise be applied to bore holes provided with a cemented casing, since `me member 32 is provided with a lplurality of radial contacting elements 33 forming a brush engaging the metallic casing 34. The conductor 3l is connected at its upper end to a conductor 35 of relatively large cross-section which passes and simultaneously at a constant rate along an extended portion of the bore hole, and obtaining tion of the bore hole, whereby the relative therm'alproperties of the earth formations surrounding said portion of the bore hole may be ascertained. v

3. The method of determining the nature of earth formations traversed by a -bore hole containing liquid, which comprises the steps of initially obtaining indications of temperature variations in an extended portion of the bore hole, generating heat uniformly and simultaneously along said bore hole portion, and subsequently obtaining indications of temperature variations in said portion of the bore hole, where-,- by the relative thermal properties of the formations surrounding said bore hole portion may be ascertained.

4. Apparatus for generating heat uniformly in an extended portion of a bore hole, comprising a U-shaped electrical heat generating conductor of considerable length, a cablefor moving said conductor through the bore hole, a 'source of electrical energy at the surface of the earth, and electrical connections in said cable for connecting said source to-said conductor.

5. Apparatus for generating heat uniformly in an extended portion of a bore hole lined with a conductive casing, comprising a heat generating over the sheave 20' at the earths surface and which is wound on the winch 2l, by means .of

which it may be raised or lowered within the bore hole i3.

The heating element 3l is energized from .the source 30 through a-Wire 36 which is connected tothe cable 35 at a point 31, the other terminal of the source 30 being connected through a wire 38 to the top of the metallic casing 3S, so that the casing 36 provides a return conductor for the heating element 3l. This embodiment operates in essentially the same manner as described above in connection with Figs. l and 3.

It will be evident from the foregoing that the invention enables the relative thermal proper-` ties of the strata traverse'dby a bore hole to be determined with a greater accuracy than has been possible heretofore. By reason of the fact that the heat is generated at a uniform rate in the drill hole and a uniform heat distributionis bore hole liquid into zones of different temperature adjacent formations vof diilerent thermal conductor of considerable length adapted to be disposed longitudinally in the bore hole, electri-` cal contact making means connected to the lower end of said conductor and engaging said bore hole casing, a source of electrical energy at the surface of the earth and electrical connections between said source and the conductor and bore hole casing. 6. Apparatus for generating ,heat uniformly in an extended portion of a bore hole lined with a metallic casing comprising a heat generating conductor of considerable length adapted to be disposed longitudinally in the bore hole, a conductive brush secured tothe lower end of said conductor and engaging the bore hole casing, a cable for moving said conductor and brush through the bore hole, a source of electrical energy atthe surface of the earth, an electrical connection in the cable for connecting said conductor to the source, and an electrical conneciiign between the source and the conductive cas- 7. The method of determining the nature of earth formations traversed by a bore hole containing a liquid, which comprises the steps of generating heat simultaneously, uniformly and at a known rate in the bore hole liquid along an extended portion ofi the bore hole, continuing the generation of heat at said points for a suilcient length of time to produce stratication of the properties, and obtaining indications of the temperature of the bore hole liquid at various points along said extended portion of the bore hole, whereby the relative thermal properties of the formations may be ascertained.

8. The method of determining the nature of earth formations traversed by a bore hole containing a liquid, which comprises the steps of providing electrical energy at a known location in the bore hole, converting said electrical energy to heat energy simultaneously along an extended portion of the bore hole, thereby generating

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